U.S. Frost Dates by Weather Station

NOAA station USC00245596 · Montana

Frost Dates for Melstone, MT

NOAA weather station Melstone (USC00245596), Montana · elevation 2932 ft (894 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 23only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season141 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Melstone, MTSpring: a frost after April 28 in 9 years out of 10, after May 10 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 29 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 141 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Sep 29Frost season at Melstone, MTSpring: a frost after April 28 in 9 years out of 10, after May 10 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 29 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 141 days.JFMAMJJASONDLast frost ~May 10First frost ~Sep 29
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.Today

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 23September 14
50% (typical)May 10September 29
90% (likely)April 28October 12
Frost-free season (32°F, 50% chance)
141 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 8 (2 days earlier than the 30-year normal), typical first fall frost October 2 (3 days later). Frost-free season 144 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Melstone: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 23, 20% May 19, 30% May 15, 40% May 12, 50% May 10, 60% May 7, 70% May 4, 80% May 2, 90% April 28. Observed last spring frost in recent years: 2021 May 22, 2022 May 22, 2023 April 23, 2024 May 4, 2025 April 18, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 23May 10Apr 282021: May 222022: May 222023: April 232024: May 42025: April 182026: May 19Fall at Melstone: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 20, 30% September 23, 40% September 26, 50% September 29, 60% October 1, 70% October 4, 80% October 7, 90% October 12. Observed first fall frost in recent years: 2021 September 17, 2022 October 15, 2023 October 23, 2024 October 13.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 29Oct 122021: September 172022: October 152023: October 232024: October 13
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021May 22September 17
2022May 22October 15
2023April 23October 23
2024May 4October 13
2025April 18incomplete record
2026May 19season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 28 in Melstone carries a 90 % chance of a light frost and is therefore a gamble. The cautious spring date for tender crops is May 23, when only a 10 % chance of a light frost remains. The 50% date is May 10, indicating a 50 % chance of a light frost later than this date, while the 50% hard-frost date is April 29.

In the fall, the cautious date to finish harvesting tender crops is September 14, with a 10 % chance of a light frost earlier. The 50% fall date is September 29, giving a 50 % chance of a light frost earlier than this date, and the 50% hard-frost date is October 7. Hard frost at 28 °F can damage plants more severely than a light frost at 32 °F because it reaches lower temperatures.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 23" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 14" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Melstone, MTNumbered nearest stations: 1 — Flatwillow, MT — 28 mi; 2 — Ingomar, MT — 32 mi; 3 — Roundup, MT — 33 mi; 4 — Hysham, MT — 37 mi; 5 — Grass Range, MT — 53 mi.25 mi · 40 km1. Flatwillow, MT — 28 mi12. Ingomar, MT — 32 mi23. Roundup, MT — 33 mi34. Hysham, MT — 37 mi45. Grass Range, MT — 53 mi5
  1. Flatwillow, MT 28 mi (45 km)
  2. Ingomar, MT 32 mi (52 km)
  3. Roundup, MT 33 mi (54 km)
  4. Hysham, MT 37 mi (60 km)
  5. Grass Range, MT 53 mi (85 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 46.6008, -107.8706.